The blue-sensitive cones of the macaque retina are selectively labelled by tissue-reactive dyes injected into the vitreous humour. We have examined the dependence of blue cone density on retinal eccentricity along the temporal and nasal segments of the horizontal meridian. We have also studied a selective staining of some postreceptoral cells. These studies provide information of the probable retinal circuitry of the blue-sensitive cone pathway of primate retina.